1. Field of the Invention
The present invention relates to an automotive seat, particularly to an automotive seat equipped with a lifter function which can adjust the level of a seat cushion.
2. Description of the Related Art
There has been a type of automotive seat which is equipped with a lifter function to adjust the level of the seat cushion. For example, Japanese unexamined patent application publication No. 2002-142908 discloses an example that a link mechanism provided under the seat pivots to rise so that the seat is lifted up by the link rise amount. In order to reduce the number of components, the components to lift up and down the seat cushion are simply constructed. The example of Japanese unexamined patent application publication No. 2002-142908 is constructed mainly by only a front link and a rear link to support the seat.
When an impact is applied to an automobile due to a low speed rear end collision, the impact is transmitted to a seat inside the vehicle. In an automobile with a mechanism to lift up and down the seat cushion, safety against the impact applied to the vehicle may be impaired depending on the mechanism. A link mechanism is considered, by way of example, in which two each links on the right and the left of the seat cushion, four in total, are provided, and one or two of them are not linked to power, or link-free, in order to simplify the mechanism and reduce the number of components. In this case, inertia force of the seat due to the collision turns the free links. Then, the seat supported in a lifted-up state above the base by the links descends abruptly so that a shock is applied to the occupant who has sat on the seat. If only the rear links of the front and rear links turn, only the rear part of the seat descends so that the occupant tilts backward and a shock is applied to the occupant.
The present invention has been accomplished in view of the foregoing circumstances and an object of the invention is to provide an automotive seat, whose seat cushion is adjustable in level up and down, with improved safety at the time of application of an impact to the vehicle.